Drive for Simplicity: Trends in AC Drives

Traditionally, the primary use of drives has been in applications such as powering pumps, fans, and conveyors. While they will continue to be used in those applications, today's end-users have a different approach to that of a decade ago.

Drives now are developed fully and, therefore, more widely accepted as a product. The need to answer the question, “What does it do?” has been replaced by the expectation that a drive will “just do it.” This shift in attitude brings with it the assumption that drives are simple to buy, install, start up, commission, own, and run.

At the same time, drives are finding new applications, such as in exercise machines, pizza ovens, honey centrifuges, and car washes. In these applications, drives are considered commodities, and original-equipment manufacturers (OEMs) who may not traditionally have used drives once again are demanding simplicity. In fact, a recent survey showed that alternating-current- (AC-) drive users rated simple controls and setups and convenient operator interfaces as “very important.”

THE QUEST FOR MINIATURIZATION

Simplicity and ease of use manifest themselves in many ways. The fact that drives can be used in domestic washing machines is a testimony to their extreme compactness. Drives have become smaller, more capable, easier to use, and cheaper by orders of magnitude.

Smaller drives are easier to install. Panel builders are able to fit more drives into a standard cubicle, enabling panels to be smaller. This allows the use of smaller and less costly control rooms. Also, drives become easier for OEMs to fit into equipment. A classic example of this is cranes, an application that always has had limited space for drives.

Reductions in drive size have resulted from the use of fewer components, greater packing density, improvements in semiconductor technology, and improved cooling techniques. In fact, there has been a tenfold decrease in the size of drives over the past 10 years.

DRIVING DOWN COST

An additional benefit to reducing component counts in drives is reduced costs. One manufacturer predicts that, over the next few years, the parts count of its drives will be reduced by approximately 20 percent through the use of integrated electronics to eliminate separate components, such as external-flash and random-access memories and analog/digital converters. Mechanical parts also are being integrated, for example, by combining frames and enclosures, allowing them to perform multiple functions.

Reducing part count also enhances reliability: Fewer parts means fewer interfaces and mechanical fixings, which often are a source of failures.

IMPROVED COOLING

Advances in the development of power semiconductors have helped to improve drives. A reduction in power losses per unit area of silicon used means that the same silicon area is able to handle more power. This has enabled the construction of smaller semiconductors and reduced the need for cooling within drives. This, in turn, allows the use of smaller heat sinks and reduced air volumes inside of drives, resulting in smaller and smaller drives. The only limitations are the terminals because these must accommodate cables that are large enough to carry sufficient current to a drive.

But it is not just the development of power semiconductors that has enabled the miniaturization of drives. Of prime importance is the technology used for cooling. Considerable research-and-development effort is being put into new cooling techniques, as well as reducing the need for cooling.

While air cooling is likely to remain the dominant technique, liquid cooling is finding increasing use in areas such as wind-power, transportation, and marine applications.

Setup is performed entirely using software functions, with uploads and downloads to and from drives.

Setup information is archived for future retrieval. To obtain the full benefit of this technology, however, operators still must refer to user's manuals. Intelligent control panels that will significantly decrease the need for paper-based manuals are in development. The secret, though, is to find an easy way to access this kind of functionality. Enter the keypad.

THE TRUE VALUE OF THE KEYPAD

Most equipment-investment decisions carry a proviso for fast installation to ensure that production will start rapidly and smoothly. The speed with which a machine can be up and running after the installation of new equipment or a maintenance shutdown is paramount. If a machine breaks down, it can cost the operator $20,000 per hour, so easy setup and commissioning are a priority. Such urgency increases the risk of errors in installation and commissioning. These can be overcome by eliminating manual intervention whenever possible. The keypad is central to this goal.

These guiding principles suggest the need for intuitive assistance. “Wizards” are aimed at guiding users through various procedures, such as maintenance, diagnostics, and startup, by asking questions in plain-text language. There are no complex parameter numbers or codes.

For an OEM that buys 4,000 AC drives per year, the time saved by using an easy startup system can be significant. Such a system can cut 15 min from the commissioning time of a drive, equating to a savings of 1,000 hr a year. For an engineer working 2,000 hr a year, that is half of a man-year.

A common look and feel allows the users to switch among different products from a given manufacturer easily, without having to go through a time-consuming learning process for each new product.

SPECIALIST HMI

Another tool that makes life easier for OEMs is a hand-held human-machine interface (HMI) that allows drive parameters to be installed in seconds. The device can be used to select and set parameters and copy configurations between drives, without even powering up a drive. No specialized knowledge is required.

APPLICATION-SPECIFIC SOLUTIONS

AC-drive users can reduce costs even more by employing application-specific drive solutions. These drives incorporate incremental functionality that supports specific applications such as fan and pump control, mixers, or crane controls. They can reduce the total cost of ownership through shorter startup times, lower integration costs, and improved machine productivity.

Time savings during commissioning can range from one to several hours. The process does not require expert programmers and, therefore, saves the considerable expense of sending commissioning engineers around the globe to fine-tune individual drives.

For example, a new pump-control software module eliminates the need for an external programmable logic controller (PLC) and can help save energy, reduce downtime, and prevent pump jamming and pipeline blocking. This software add-on for industrial drives contains all of the common functions needed by water and waste utilities, industrial plants, and other pump users through six pump-control functions.

The software also incorporates an adaptive programming utility, enabling users to customize drives for specific applications. This utility consists of a set of simple-to-use blocks that can be programmed to perform any operation from a predefined set of functions. All common mathematical and logical functions, as well as switches, comparators, filters, and timers, are available. These days, users can have the power of a small PLC inside of their drive.

A further breakthrough is that programming can be carried out using a standard control panel. No special hardware or software programming tools are needed. As a result, programming takes only a few minutes and can be carried out on site, during commissioning.

Ilpo Ruohonen, Mika Paakkonen, and Mikko S. Koskinen lead product development for the global drives business of ABB Oy.